1. Field of the Invention
This invention is in the field of propulsion systems, such as rocket motor propulsion systems.
2. Description of the Related Art
There are launch systems, missiles, rockets, and projectiles that require a propulsion unit that either mounts in front of other units, or straps to a main propulsion unit to be separated after use. An example of the first type is an escape module for a booster rocket, such as the launch escape assembly for the Apollo Saturn V rocket. Another example of the first type is in wire-guided missiles, where a missile motor is located in front of a spool of fiber optic wire. An example of the second type of motors is used in ejection seats of aircraft.
In such systems output from a standard rocket motor nozzle cannot be directed straight rearward, since to do so would cause a plume of very hot exhaust gases to contact other structures. To remedy this problem nozzles in such prior art propulsion systems have been canted. That is, the nozzles have been angled away from a centerline of the vehicle.
FIG. 1 shows a prior art launch escape assembly 10 used for separating a crew module 12 from a main rocket (not shown) in the event of a malfunction during launch or early in the flight procedure. The launch escape assembly shows two types of canted nozzle arrangements used in prior systems. A main launch escape motor 16 has a set of canted nozzles 18 at its aft end. The launch escape motor canted nozzles 18 are located behind an aerodynamic skirt 20, and protrude beyond the diameter of the cylindrical launch escape motor 16. The launch escape assembly 10 also has a tower jettison motor 24 that has canted nozzles 26 that are substantially flush with an outer surface of the main cylindrical part of the launch escape assembly 10. The tower jettison motor 24 is located toward a forward end of the launch escape assembly 10, near a nosecone 30 and a canard assembly 32.
The launch escape assembly 10 also includes a launch escape tower 36, used to maintain separation between the launch escape motor canted nozzles 18 and the crew module 12. Although the launch escape motor canted nozzles 18 are angled somewhat away from the centerline of the launch escape assembly 10, some additional separation is required to avoid undesirable heating of the crew module 12.
The two types of canted nozzles 18 and 26 illustrate some of the shortcomings of prior art propulsion systems that are placed forward relative to other components. The launch escape motor canted nozzles 18 require a diameter greater than that of the main cylindrical portion of the launch escape assembly 10. And despite being angled away from the centerline of the launch escape assembly 10, an additional structure (the launch escape tower 36) is still necessary to provide separation from the crew module 12. The launch escape tower 36 adds additional cost and weight, and increases the overall size of the launch escape assembly 10.
Although the tower jettison motor canted nozzles 26 are substantially flush with the outer cylindrical surface of the main portion of the launch escape assembly 10, this feature is achieved at a performance cost. Truncating the canted nozzles 26 reduces overall performance when compared to converge-diverge nozzles that do not have truncated shapes.
From the foregoing it is seen that there is room for improvement with regard to propulsion systems of this type.